To make the meringue, melt the chocolate in a heatproof bowl over a pan of simmering water, or in quick bursts in the microwave. Allow to cool. Mix together the sugar, cream of tartar and cornflour.

Put the egg whites in a stand mixer or a metal or ceramic bowl. Using an electric whisk, whisk on a low-medium speed for a few mins until stiff peaks form, then slowly start to add in the sugar mixture, 1 1/2 tbsp at a time, whisking between each addition until the sugar has dissolved and is well incorporated into the meringue. Once you have a thick, glossy meringue that holds its shape on the whisk, pour over the melted chocolate and swirl it in so you have a rippled meringue – avoid overmixing to retain the swirl effect.

Heat the oven to 120C/100C fan/gas 1/2 and use a little of the meringue mix from the whisk to stick some baking parchment to two baking sheets, then dollop on little mounds of meringue, or, if you prefer, make a nest shape by flattening the meringue down with the back of a spoon. Bake the meringues for 1 hr 10 mins until crisp and pulling away from the parchment. Leave to sit in the oven until completely cool.

Meanwhile, weigh out 150g of the blackberries and put in a non-reactive pan (such as stainless steel) with the sugar and bay leaves. Cook over a gentle heat for a few mins, stirring so that the blackberries start to break down into a loose compote and release their juice. Leave the mixture to cool, then stir through the remaining blackberries. Set aside.

Whip the cream until soft peaks form, then fold through the natural yogurt. Swirl through a couple of spoonfuls of the blackberry and bay juices so you have a ripple effect. Add a spoonful of the cream mixture to each meringue and spoon over the blackberries and their juices. Discard the bay leaves. Best eaten on the day of baking.